Immersion ultrasonic inspection system of the whole surface of rolled flat bar

ABSTRACT

The immersion ultrasonic inspection system inspects the whole surface of a rolled flat bar specimen including flat and end portions thereof by immersing the specimen and probes in water and applying surface wave to the specimen by a plurality of probes disposed in the front and back sides of the specimen at the different points with inclination to the surface of the specimen.

11R 318500027 I \J v Y r i' F United States K 3 j 11 3,850,027 Nakanishiet al. Nov. 26 1974 X I 1' t 1- 5 1 IMMERSION ULTRASONIC INSPECTION [56]References Cited SYSTEM OF THE WHOLE SURFACE OF UNITED STATES PATENTSROLLED FLAT BAR 2,524,208 10/1950 Piper 73/67.6 [75] I Inventors: AkitoNakanishi, Nishinomiya; 3124154 12965 Loving 5 X Hisashi Nakazawa,Akashi; 3,285,059 11/1966 Bogle 73/67.) Kazuyosh-l Yamashima, 3,364,7323 1/1968 Sasaki 73/67.8 S Nishinomiya; Toshio Shiraiwa, OTHERPUBLICATIONS Ikoma; Yamaguchi Akashh Surface Waves at UltrasonicFrequencies" by Cook of Japan et al., ASTM Bulletin, May 1954, pages8l84. [73] Assignee: Sumitomo Metal Industries, Ltd., Osaka, JapanPrimary Examiner-James .1. Gill Filed: Mar- 1973 Attorney, Agent, orFzrmKurt Kelman [21] Appl. No.: 337,711 [57] ABSTRACT The immersionultrasonic inspection system inspects 0 Foreign Application priorityData the whole surface of a rolled flat bar specimen including flat andend portions thereof by immersing the Mar. 9, 1972 Japan 47-23567Specimen and probes in water and pp y g Surface wave to the specimen byaplurality of probes disposed g 'g gg gi in the front and back sides ofthe specimen at the dif- [58] Field 8 S 67 8 R ferent points withinclination to the surface of the 73/715 U, 67.9, 67.7 Specimen 8Claims, 16 Drawing Figures Pmtmm z 3.850.027

SHEET 30F 5 TRAVERSE DIRECTION WATER LEVEL 42 Fig. 8

bUl

NORMAL DISPLACEMENT FOR SURFACE AMPLITUDE I5.- 20 {-UEPTH FROM SURFACEIMMERSION ULTRASONIC INSPECTION SYSTEM OF THE WHOLE SURFACE OF ROLLEDFLAT BAR BACKGROUND OF THE INVENTION The present invention relates to asystem for detecting surface flaws over the whole surface of a flat barincluding flat and end portions thereof using surface wave propagationin an immersion ultrasonic inspection method.

With the development of the sutomobile industry the demand for rolledspring steel flat bars has increased and, at the same time, betterquality and reliability have been required making precise and reliableinspection indispensable.

In detecting defects on the surface of rolled spring steel flat bars ithas become a common practice to find flaws visually. Other methods, suchas ultrasonic inspection and eddy current inspection, have been employedonly in the limited region. Heretofore, however, an advanced inspectionsystem capable of automatically inspecting the whole surface of the flatbar including the end portions thereof at high accuracy and ateconomical speed has not been developed in the art.

Accordingly, an object of this invention is to provide an immersionultrasonic inspection system for automatically and efficientlyinspecting the whole surface of the rolled flat bar including the flatand end portions thereof at high accuracy.

Another object of this invention is to increase the inspection accuracyby preventing bubbles from attaching to the surface of specimen byspraying water under pressure onto the whole surface of the specimen toforcibly prewet the whole surface immediately before introducing thespecimen into immersion tank.

A further object of this invention is to increase the inspectionaccuracy by preventing bubbles from attaching to the ultrasonictransmitting and receiving surface of probes disposed within theimmersion tank by spraying water under pressure onto the surface.

A still further object of this invention is to provide a probepositioner for freely controlling the distance, angle of inclination,horizontal and vertical positions of the probes disposed within theimmersion tank.

SUMMARY OF THE INVENTION From the fact that displacement energy ofsurface wave concentrates in the depth of several wavelengths from thesurface of the flat bar, it is generally known that the inspectionsensitivity is high for the flaw immediately below the surface and thatthe surface wave has a tendency to get around the end portions of theflat bar. Applying this phenomenon to immersion inspection, thisinvention has developed a high speed and stable immersion inspectionsystem for detecting flaws on the whole surface of the rolled flat barincluding rolled spring steel flat bar.

The immersion ultrasonic inspection system according to the presentinvention has an inlet table, side guide rollers, pinch rollers, a flawdetector (water tank, probe positioner, etc.), and an outlet tabledisposed in series on a transfer line of rolled flat bars of, forexample, rolled spring steel flat bar, A specimen of the rolled flat baris introduced into the immersion tank. probes are disposed in both frontand back sides of the specimen in inclined relation thereto atrespectively different points of incidence within the immersion tank,and a surface wave is applied to the specimen from the probes to detectflaws on the whole surface of the specimen including the flat and endportions thereof.

The specimen prewetting means according to this invention has a set ofnozzles inclined from the upper and lower directions at the neighborhoodof the specimen inlet of the immersion tank of the flaw detector. Theprewetting means prevents bubbles from attaching to the surface of thespecimen by spraying water under pressure onto the surface thereof fromthe nozzles. A tank for receiving water leaking from the nozzles and theimmersion tank may be provided so that the received water is returned tothe immersion tank by a suitable pump.

The bubble removing means of the immersion type probe according to thisinvention removes bubble attaching to the ultrasonic transmitting andreceiving surface of the probe immersed in the water by spraying waterunder pressure onto the ultrasonic transmitting and receiving surface ofthe (immersion type) probe.

The probe positioner according to this inventio mgging a set of prob e sspaced apart from and retained opposite'to e'ach other can cqitrgldjstanee between the @bes. vertical and liifiz ontal positions andangles of i iiiiation of the probes.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be betterunderstood from the following description taken in connection with theaccompanying drawings in which:

FIG. 1 is a side view showing a schematic construction of the immersionultrasonic inspection system according to the present invention;

FIG. 2 is a partial sectional view taken along the line IIII of FIG. 1;

FIG. 3 is a schematic constructional view taken along the line IIIIII ofFIG. 2;

FIGS. 4A-4D are a side view and plan views of the bubble removing meansof the probe;

FIGS. 5 and 6 are schematic illustrations of the arrangement of theprobes;

FIG. 7 is a side view of the probe positioner;

FIG. 8 is a graph explaining the energy displacement of surface wave;

FIG. 9 is a schematic illustration of the inclined disposition of theprobe;

FIG. 10 is a graph showing the relation between the angle of inclinationof the probe and the echo height;

FIG. 11 is a graph showing the relation between the inspection distanceand the attenuation of echo;

FIG. 12 is a schematic illustration of an arrangement for testing theeffect of the shape of the end of specimen on the end echo; and,

FIG. 13 is a graph showing the relation between the shape of the end ofspecimen and the echo height.

DESCRIPTION OF THE PREFERRED EMBODIMENTS A preferred embodiment of theimmersion ultrasonic inspection system according to the presentinvention will now be described. FIG. 1 is a side view showing aschematic construction of the immersion ultrasonic inspection system 1comprising an inlet table 2, a set of pinch rollers 3, a flaw detector4, and an outlet table 5.

A specimen 10 is transferred in the longitudinal direction 11 bytransfer rollers 21 and side guide rollers 22 mounted on the inlet table22 and reaches the first pinch rollers 3, whereat the specimen 10 iscontrolled in horizontal position by side guide rollers 22 andcontrolled in vertical position and transferred to the flaw detector 4to be described. The specimen having passed the flaw detector 4 isreceived by the second pinch rollers 3 to be controlled in verticalposition and then transferred to the succeeding outlet table 5. Thespecimen is further transferred in the longitudinal direction 1 1 bytransfer rollers 51 and side guide rollers 52 mounted on the outlettable 5.

In order to increase the inspection efficiency it is preferable totransfer in the longitudinal direction a plurality of specimens (twobars in this embodiment) disposed in parallel to each other. This iseasily achieved by using the side guide rollers suitably.

The first and second pinch rollers 3 are in the same constructioncomprising a set of pinch rollers 31 vertically spaced from each other.The specimen 10 passes through the set of pinch rollers.

The flaw detector 4 comprises an immersion tank 41, probe positioners42, probes 43, and receiving rollers 44. As shown in FIGS. 2 and 3, twospecimens 10 disposed in parallel are transferred from the first pinchrollers 3 to the flaw detector 4, introduced into the immersion tank 41through an inlet 411 and transferred out through an outlet 412. In theimmersion tank, the specimens 10 are supported by the receiving rollers44 and immersed within the water, and are disposed, as shown in FIGS. 2and 3, so as to be detected from the upper and lower directions by aplurality of probes 43 which are, as detailedly described hereinbelow,adjustably mounted to the probe positioners 42.

In the immersion ultrasonic inspection system using water as the mediumof ultrasonic waves, specimens are introduced into the immersion tankand inspected within the water. When the specimen is introduced into thewater at high speed, an air layer is formed between the specimen and thewater making thereby projection of ultrasonic wave difficult and normalinspection impossible. Since ultrasonic surface wave reflects verysensitively minute roughness on the surface to be inspected, even thepresence of a minute air bubble reflects ultrasonic surface wave. In theimmersion tank, surface of the specimen is normally in the completelywet condition. Heretofore, however, when several small air bubbles areremaining attached on the surface, not only the surface flaws but alsosuch air bubbles are detected thereby decreasing the inspection accuracyand to make the judgement of the flaws difficult.

Accordingly, it is essential to increase the affinity (or attachment) ofthe specimen for water by, for example, forcibly prewetting the wholesurface of the specimen by spraying water under pressure onto thespecimen before introducing the specimen into the immersion tank.Prewetting prevents the formation of an air layer between the surface ofthe specimen and water, attachment of air bubbles or other materials tothe surface of the specimen and leakage of water of the tank through thespecimen inlet of the tank.

In order to meet this necessity, in this invention, as shown in FIG. 3,nozzles 45 are provided at the entrance side of the inlet 411 of theimmersion tank 41 for spraying water under pressure toward said inlet411 from the upper and lower directions. The water sprayed by thenozzles 45 wets both upper and lower sides of the specimen 10 whenentering the immersion tank 41 after passing through the first pinchrollers 3, while cleaning the dusts on the surface of the specimen awaywith its pressure. Accordingly, when the specimen 10 is introduced intothe immersion tank 41, the surface of the specimen 10 has the affinityfor the water of the immersion tank and, therefore, is free from theattachment of air bubbles. At the same time, the water under pressuresprayed from the nozzles 45 prevents leakage of water from the inlet 411of the immersion tank 41.

The pressure of water about 3 5 Kg/cm is sufficient for thefunction ofthe nozzles 45. A portion of the sprayed water is transferred togetherwith the specimen 10 into the immersion tank 41. The rest of the wateris, received by a tank 46 provided below the immersion tank 41, and isrecirculated by a circulating pump 47 into the immersion tank 41together with the water overflowed from the tank 41.

Further, in the immersion ultrasonic inspection system, air bubblesfloating within the water or attached to the surface of the specimenfrequently attached to the ultrasonic transmitting and receiving surfaceof the probe within the water causing decrease in inspection sensitivityand generation of noise resulting in decrease in accuracy or reliabilityof flaw detection. Accordingly, it is necessary to increase thereliability of the flaw detection by removing the air bubbles from theultrasonic transmitting and receiving surface of the probe disposedwithin the immersion tank.

In the present invention, in order to meet this necessity, a ring-shapednozzle pipe 432 is provided at the position opposite to and somewhatspaced from the ultrasonic transmitting and receiving surface 431 of theprobe 43, as shown in FIG. 4A. The ring formed at the leading end of thenozzle pipe 432 has a diameter somewhat larger than the outer diameterof the probe body 43 as shown in FIG. 4B, and is connected and supportedat several points to a fixture 434 by supports 433 so that the center ofthe probe 43 is coaxial with the center of the ring formed by the nozzlepipe 432. On the inner side of the ring of the nozzle pipe 432 there areprovided a number of orifices 435 so that, during injection, water underpressure injected from the orifices 435 is uniformly applied to theultrasonic transmitting and receiving surface 431 of the probe 43disposed above the ring. Even when the probe 43 i s op- Hating .transm.t;t iqjsssive-t e t t tsomcla st water T152181 a predetermined pressureis continuously injected from the orifices 435 toward the centralportion of the transmitting and receiving surface.

While the nozzle pipe 436 in the preferred embodiment of this inventionis described to be a copper pipe of diameter about 5 6 mm havinginjection orifices of diameter about I 1.5 mm, it is to be clearlyunderstood that the nozzle pipe of this invention is not limited theretoor thereby. The nozzle pipe of this invention is not limited also inshape to the ring as shown in FIG. 48. But it can be formed insemi-circle configuration as shown in FIGS. 4C and 4D or in anypolygonshape as desired. In any of such shapes other than the ring, theeffect similar to that of said embodiment can be achieved by applyingwater under pressure injected from the nozzle uniformly onto theultrasonic transmitting and receiving surface of the immersion typeprobe.

Since the inspection system according to the present invention employsimmersion ultrasonic inspection system, it is preferable to dispose theprobes as shown in FIGS. 5 and 6 considering the attenuation of surfacewave with distance within water. Namely, a plurality of probes (threeprobes in this embodiment) are disposed on the both front and back sidesof the specimen 10 in inclined relation to the vertical direction by apredetermined angle 0i as described in detail hereinbelow so that thefull width of the specimen 10 can be covered by the probes.

Referring now to FIG. 7, the construction of a probe po s itioner 42 fordetermining and maintaining "the probes is d s cribed. A probe 43a forinspecting the front side and a probe 43b for inspecting the back sideare attached respectively to support arms 421a and 421!) spacedvertically from each other. The position of probes 43a and 43b arecontrolled in angle with respect to the vertical direction respectivelyby handles 422a and 422b, in vertical space therebetween by a handle423, and in horizontal position, namely the position in widthwisedirection of the specimen by an handle 424. It is preferable that thecontrol of these angle of inclination. length of space, and vertical andhorizontal positions is indicated in suitable scales. More detaileddescription of the probe positioner will be unnecessary to the skilledin the art in working this invention.

In FIG. 6, there are shown three stages (No. 1, No. 2, and No. 3) of theprobe positioners 42 disposed along the advancing direction of thespecimen 10.

Now, the determination of angle of incidence of the probes is described.

From the fact that displacement energy of a surface wave generallyconcentrates in the depth of several wavelengths from the surface of thespecimen as is obvious from FIG. 8, it is known that the inspectionsensitivity is high for the flaw immediately below the surface and thatthe surface wave has a characteristic property to get around beyond thecomer of the specimen.

Taking advantage of this phenomenon, the inventors experimentallyobtained the relation between the angle of incidence of ultrasonic waveand the echo height in the arrangement and dimension shown in FIG. 9using lead zirconate vibrator of frequency 2.25 MHz having the diameterof 19 mm. In FIG. 9, the probe 43 is inclined with respect to thevertical direction by the variable angle 61', the distance between theultrasonic transmitting and receiving surface 431 of the probe 43 andthe point of incidence 12 on the surface of the specimen 10 is fixed to50 mm, the distance between the point of incidence l2 and the surfaceflaw 13 of the specimen 10 is determined as 50 mm, and the distancebetween the surface flaw I3 and the end portion of the specimen 10 isdetermined as mm. The surface flaw 13 was made artificially byelectrodischarge machining to the depth of0.5 mm on the flat portion ofthe specimen.

The results of the experiment are shown in FIGS. 10 and 11. As obviousfrom FIG. 10, the detection accuracy is highest (or attenuation of echois smallest) when the angle of incidence is about 30 and it correspondswell to the calculated value 307 (30.11). The angle at which reflectionecho (noise echo) from the end portion is difficult to emit is 2936(296), a little acuter than the theoretical angle of incidence 30? (30.11). The attenuation of echo by a V notch 13 (see HG. 9)

artificially made at 20 mm from the end portion is as shown in FIG. 11.The echo attenuates functionally with distance and its attenuation is6.16 dB/cm. However, this problem can be easily solved by using anautomatic compensation circuit of attenuation by distance as describedhereinbelow.

FIG. 13 shows the results of examination of the effect of the endreflected echo, namely using specimens having different end shapes (Rfinish and angle finish). As seen from FIG. 13, the reflection islargest when the angle finish in 90, and with R finish the surface wavepropagates along the curvature and there is little reflection from the Rportion. It is interesting to find that practical spring steel flat barshaving the rolled R finish end and the angle finish end of show almostthe same reflection.

The inspection result detecting circuit to be connected to the probe,may-be a known ultrasonic inspection circuit comprising a synchronouscontroller, a horizontal axis sweep. a pulse generator, a receivingamplifier, a cathode-ray tube, and a source of power. The results ofdetection are displayed on the cathode ray tube or automaticallyrecorded on for example a pen-writing oscillograph for observation.

An electric pulse synchronously controlled by the source frequency orany specific frequency is applied to the probe and converted into anultrasonic pulse by an electrostriction vibrator of the probe, and thesurface wave is made incident as an ultrasonic wave on the surface ofthe specimen. When the surface wave propagating on the surface of thespecimen reaches a defect such as a flaw, it is reflected at that pointand received by the probe, converted back into an electric pulse,amplified at the receiver, detected, indicated on the sweep trace of thecathode-ray tube, whereby the size of the flaw.is det e c ted. Since theattenuation of the surface wave is heavily influenced by the quality ofthe surface finish, flaw detection can be made easier by finishing thesurface of the specimen well. In order to 40 makethgquantitativeevaluation of the flaw further efficient, the detectioncircuit of the inspection system according to the present inventionincludes a distance compensation circuit and a level automatic controlcircui t for regulating the attenuation of the ultrasonic 5 wave touniformly evaluatethgflayvs detected at various portions of thespecimen. In the system according to the present invention, when sodesired, a delay circuit coupled with a marking device may be providedfor automatically marking the flaw after the water is removed from theinspected specimen.

On thespecimens having for example two different dimensions, namely 76.2mm width X l 1.35 mm thickness X 5,000 mm length and 88.9 mm width X12.67 mm thickness X 5,000 mm length, an artificial flaw of 0.3 mm depthis made at the end portion. Thereafter, the inspection sensitivity ofthe system is established so that the echo height of the artificial flawis 35 mm on the cathode-ray tube and continuous inspection is ren deredat this sensitivity. Then, the inspection system can clearly detectnatural flaws of 0.1 1 mm 0.23 mm depth on the flat portion andartificial flaws of 0.08 mm 0.44 mm depth on the end portion. Othersmaller flaws such as lap and scratch of, for example, 50 u depth can bedetected by increasing the inspection sensitivity.

Table I shows the results of the practical flaw detection at thesensitivity described above.

Number of Number of flat bars rejected Number of flat bars by UltrasonicInspection flat bars accepted Remark inspected by Ultra Total Crack LapScratch Roll sonic lnsp.

.50 6,949 6,427 522 193 279 32 I8 B20 mm width (Note) Three probes areapplied each on the front and back sides of the specimens.

As is obvious from Table l, in the inspection with the describedsensitivity a harmful crack is not overlooked whereas harmful lap androll flaws (not less than 0.2 mm in depth) are 100 percent detectedthough the detection sensitivity is varied with the shape of the flawsand the direction of incidence of ultrasonic wave. it may be added that522 sheets of flat bars rejected by the ultrasonic inspection were allallowed after the flaws were removed by grinding.

The automatic surface flaw detection system of rolled steel baraccording to the present invention has been used for'inspecting flatbars having the dimension 50 120 mm width X mm thickness X 4,000

6,500 length, at 21 highest rate 90 m/min (nominal rate: 25

60 70 m/min). In other words the system can continuously inspect twosheets of flat bars 6,000 mm long in eight seconds.

While the above preferred embodiment is shown used in an immersion tank,it is possible to. achieve the same effect as in the above embodiment byusing a laminar flow water nozzle instread of the immersion tank so thatan ultrasonic transmitter (or a probe) is disposed within the laminarflow water nozzle and the ultrasonic wave is propagated within saidnozzle.

As described above, in the method of the present invention, since theprewetting means of high power is 'provided prior to the partialimmersion tank to increase the attachment of water to the rolled flatbar and simultaneously to cool it effectively, the present invention hasan advantage that the specimens immediately after hot rolling can becontinuously inspected in satisfactory condition without generating airbubbles or steam if only the surface temperature is not higher than 80Cwithout the necessity of waiting until the specimen is completelycooled.

According to the present invention, efficiency and accuracy of surfaceflaw detection of rolled flat bars such as spring steel flat bar forautomobile construction are considerably increased, number of inspectorscan be decreased, and inspection cost can be reduced.

While we have shown and described specific embodiments of our invention,it will be understood that these embodiments are merely for the purposeof illustration and description and that various other forms may bedevised within the scope of our invention, as defined in the appendedclaims.

We claim:

1. An immersion ultrasonic inspection system which comprises incombination:

A. an immersion tank containing a liquid medium with means formaintaining a liquid level;

B. inlet means below the level of the liquid medium for introducing aflatbar to be inspected into the liquid medium and exit means below thelevel of the liquid medium for removing the flat bar therefrom;

C. liquid medium projecting means disposed for projecting liquid to saidinlet for prewetting a flat bar passing therein;

D. a plurality of probes disposed on opposite sides of the flat bar tobe inspected, said probes disposed within the immersionjank forprojecting ultrasonic i i sl tii lllQ flat q fac sheba ET flat bartransferrih g riieans provided with guide rolls for transferring the barto be inspected into the immersion tank and thereafter transferring thebar out of the immersion tank; and

F. electric circuit means for detegtingthe-inspectiQL rmfi ll the pro 5.

2. i m rfiersion ultrasonic inspection system of the whole surface ofrolled flat bar, according to claim 1, characterized in that the probesfor particularly inspecting the end portion of the flat bar among theplurality of probes disposed both in the front and back sides thereofhave the angle of incidence such that end echo is difficult to emit,preferably 2936 (29.6).

3. An immersion ultrasonic inspection system of the whole surface ofrolled flat bar, according to claim 1, characterized in that the flatbar transferring means is provided with a set of pinch rollersadjustably mounted thereon vertically spaced apart from each other andfunctions to control the vertical position of the flat bar transferredand introduce the flat bar properly into the immersion tank.

4. An immersion ultrasonic inspection system of the whole surface ofrolled flat bar, according to claim 3, characterized in that the flatbar transferring means is provided with an inlet table and an outlettable, on said tables being disposed transfer rollers and side guiderollers with suitable distance therebetween for transferring a pluralityof flat bars in parallel to each other simultaneously.

5. An immersion ultrasonic inspection system of the whole surface ofrolled flat bar, according to claim 1, further comprising:

nozzles for spraying water under pressure toward the flat bar inlet ofthe immersion tank from the both upper and lower directions; and,

a pressure-regulatable feed-water system for feeding water underpressure continuously to the nozzles.

6. An immersion ultrasonic inspection system of the whole surface ofrolled flat bar, according to claim 1, further comprising a ring-shapednozzle mounted around each probe, said nozzle having a number ofinjection orifices arranged so that the water under pressure injectedfrom the orifices is focused uniformly onto the ultrasonic transmittingand receiving surface of the immersion probe, and said nozzle beingcontinuously supplied with water under pressure from thepressure-regulatable feed-water system.

each onto support arms movably spaced vertically apart, means disposedfor regulating the angle of the probes in the vertical directionrelative a bar passing therebetween, and means for positioning theprobes in the horizontal direction relative a bar passing therebetween.

1. An immersion ultrasonic inspection system which comprises incombination: A. an immersion tank containing a liquid medium with meansfor maintaining a liquid level; B. inlet means below the level of theliquid medium for introducing a flatbar to be inspected into the liquidmedium and exit means below the level of the liquid medium for removingthe flat bar therefrom; C. liquid medium projecting means disposed forprojecting liquid to said inlet for prewetting a flat bar passingtherein; D. a plurality of probes disposed on opposite sides of the flatbar to be inspected, said probes disposed within the immersion tank forprojecting ultrasonic surface waves onto flat surfaces of the bar; E.flat bar transferring means provided with guide rolls for transferringthe bar to be inspected into the immersion tank and thereaftertransferring the bar out of the immersion tank; and F. electric circuitmeans for detecting the inspection results of the probes.
 2. Animmersion ultrasonic inspection system of the whole surface of rolledflat bar, according to claim 1, characterized in that the probes forparticularly inspecting the end portion of the flat bar among theplurality of probes disposed both in the front and back sides thereofhave the angle of incidence such that end echo is difficult to emit,preferably 29*36'' (29.6*).
 3. An immersion ultrasonic inspection systemof the whole surface of rolled flat bar, according to claim 1,characterized in that the flat bar transferring means is provided with aset of pinch rollers adjustably mounted thereon vertically spaced apartfrom each other and functions to control the vertical position of theflat bar transferred and introduce the flat bar properly into theimmersion tank.
 4. An immersion ultrasonic inspection system of thewhole surface of rolled flat bar, according to claim 3, characterized inthat the flat bar transferring means is provided with an inlet table andan outlet table, on said tables being disposed transfer rollers and sideguide rollers with suitable distance therebetween for transferring aplurality of flat bars in parallel to each other simultaneously.
 5. Animmersion ultrasonic inspection system of the whole surface of rolledflat bar, according to claim 1, further comprising: nozzles for sprayingwater under pressure toward the flat bar inlet of the immersion tankfrom the both upper and lower directions; and, a pressure-regulatablefeed-water system for feeding water under pressure continuously to thenozzles.
 6. An immersion ultrasonic inspection system of the wholesurface of rolled flat bar, according to claim 1, further comprising aring-shaped nozzle mounted around each probe, said nozzle having anumber of injection orifices arranged so that the water under pressureinjected from the orifices is focused uniformly onto the ultrasonictransmitting and receiving surface of the immersion probe, and saidnozzle being continuously supplied with water under pressure from thepressure-regulatable feed-water system.
 7. An immersion ultrasonicinspection system of the whole surface of rolled flat bar, accoRding toclaim 6, characterized in that the ring-shaped nozzle is formed in asemi-circle.
 8. An immersion ultrasonic inspection system of the wholesurface of a rolled flat bar according to claim 1 wherein a set of upperand lower probes are mounted each onto support arms movably spacedvertically apart, means disposed for regulating the angle of the probesin the vertical direction relative a bar passing therebetween, and meansfor positioning the probes in the horizontal direction relative a barpassing therebetween.